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bino/quadroculars?

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#51 GlennLeDrew

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Posted 01 September 2017 - 10:42 AM

After having used my 18" bino-Dobson for over a year now and having compared it extensively with other instruments, including a 27" mono-Dob, I can confirm that a 18" bino is at least equal, if not superior to a 25" mono. On faint objects I was even able to discern more detail than in the 27". Not only because the binocular summation factor is 1,42 (and not 1,18 as stated above), the increased contrast, more relaxed observing experience and reduced signal to noise ratio increase the summation factor to even 1,8x on those objects. I just have to close one eye to see the difference with a 18" mono and that difference is HUGE. If it were only 1,18x that difference would hardly be visible.

Also I'd like to clarify a misunderstanding. Counting in shipping and customs I paid significantly LESS for my binos than I would have paid for a 25" Obsession. Then again, double eyepieces and filters add to the expense...

Peter

Peter,

Yes, the binocular summation factor is indeed 1.414. Signal to noise is increased by this ratio. You can see point sources 1.414 times fainter. You can discriminate subtle contrast 1.414 times better. Which equates to a mono aperture 1.189 times larger.

 

You can verify this by seeing how much fainter a star you can pick out. Theory predicts 0.37 magnitude, which is a tad better than most folks actually obtain. By characterizing the equivalent aperture ratio of factor 1.414 you are in effect claiming 0.75 magnitude, which would be astonishing to say the least.


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#52 PeterDob

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Posted 01 September 2017 - 11:39 AM

No, it equals a mono aperture 1,414x larger. Hence an 18" bino equals at least a 25" mono, both with regards to light gathering power and resolution. To my experience, on faint objects, you can even make that 30"-32", without having the much higher minimum magnification (due to exit pupil).

 

EDIT: 1,18x wouldn't be logical. A binoscope has twice the amount of aperture, so 1,414x the diameter of a monoscope.

Peter


Edited by PeterDob, 01 September 2017 - 11:58 AM.


#53 GlennLeDrew

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Posted 01 September 2017 - 09:07 PM

No, it equals a mono aperture 1,414x larger. Hence an 18" bino equals at least a 25" mono, both with regards to light gathering power and resolution. To my experience, on faint objects, you can even make that 30"-32", without having the much higher minimum magnification (due to exit pupil).

 

EDIT: 1,18x wouldn't be logical. A binoscope has twice the amount of aperture, so 1,414x the diameter of a monoscope.

Peter

Our visual system does not simply add the two images together to result in what would effectively be a doubling of brightness, which an effective increase in aperture of ratio 1.414 implies. The two images each contain their unique component of visual system noise, which is also integrated along with the two signals. The noise is averaged, and the signals are averaged, which results in the root two improvement in signal to noise.

 

Try to assess for yourself the differences in limiting magnitude at some selected exit pupil, with both eyes in use vs just one. I predict it will not differ much from 1/3 magnitude. As I noted, a 1.414 gain in signal to noise theoretically provides a boost to point source limiting magnitude of 0.37 magnitude, which corresponds to a linear aperture ratio of 1.189, which is an areal ratio of 1.414.

 

You and others are misconstruing the 1.414 figure for S/N gain, which equates to the same value in effective aperture *area*, for the *linear* aperture equivalent. A 19% increase in linear aperture provides 41% more area and hence 41% fainter detection. This is the result for our visual systems, just as it is for digital image integration of two same-exposure frames as done by legions of astro imagers.

 

The visceral improvement realized by two-eyed viewing might *seem* to suggest gains that could be equivalent to an aperture doubling, but both signal theory and direct observation that quantifies beyond the level of superficial impressions refute this.

 

Again, test your own stellar limiting magnitude...


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#54 PeterDob

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Posted 02 September 2017 - 03:42 AM

No, what you're saying is incorrect. Our brain does add the two images, doubling the brightness. Actually, observing with both eyes does even MORE! Due to the fact that "false" light signals are less likely to be accepted as "true" by both eyes at the same time, contrast increases greatly and that's why on faint objects a binoscope performs like a telescope up to 1,8x its diameter!

You shouldn't focus on the limiting magnitude test because that's never going to be accurate. The best way to convince yourself is putting a binoscope next to a much bigger monoscope and see the difference. According to your reasoning, my 18" binos perform like a 21" mono. In reality, during the first light which I refer to in my article, it blew two high-quality 20" right out of the water (as can be testified by about 20 people). There simply was no comparison at all!

I suggest that you go to a star party where there's a big bino and see for yourself.

Peter


Edited by PeterDob, 02 September 2017 - 06:22 AM.


#55 GlennLeDrew

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Posted 02 September 2017 - 07:56 AM

I've looked through Newtonian 12.5" binos. And oodles of refractor binos up to 5" aperture. I've built numerous binos. Indeed, my love of bino observing ensures I'd rather a small bino than a big mono scope. But the objectively determined gains are more modest than visual impressions would suggest.

 

If the gains you find were to be true, the same must attend for any size instrument, and even the naked eye. Because in all instances our brain is presented with two nominally similar images to integrate. When you gaze at either a daytime or nighttime scene with unaided eye, do you find the same profound difference in performance? Is there a difference between your eyes, such that your dominant eye used during mono observing has lesser ability? In such case I can see where the bino summation gains will exceed those when the two eyes are rather more on the similar side.

 

For the majority who possess eyes which do not differ too greatly, the 41% improvement in the discrimination of subtle contrast is profound enough when it makes the difference between detection or not. It does not require a doubling. After all, as noted, the root two gain is equivalent to 0.37 magnitudes. We can probably say this is akin to dimming the sky by about that same value. And so a 21 MPSAS sky for the monoscopist, for the purposes of contrast discrimination, becomes for the bino observer as though being 21.37 MPSAS. Or, that a threshold object has been brightened by 0.37 magnitudes. That's no small thing. In either case, we don't see this as a darkening of the sky or a brightening of the object. We are really seeing a lessening of the interfering noise that results in a 'cleaner', better defined view. It just appears that the object's have gotten a bit brighter as compared to the sky. But that's the natural consequence of noise reduction.


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#56 PeterDob

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Posted 02 September 2017 - 08:43 AM

The difference with the unaided eye seems small because the light gathering power of our eyes is so small. Especially during daytime the difference is absolutely zero because when closing one eye our brains (and the remaining eye) adjust to get the correct light sensitivity for that particular situation. The same goes during the night and I'd like to challenge you to do a limiting magnitude test with one or both eyes, as you suggest. When observing with a binoscope or binoculars, have you ever tried to close one eye? The difference is simply huge! This isn't about "impression", but about real gains. Otherwise, how would you explain that NGC6905 showed very little detail in the 20" whereas in the binoscope it appeared as in the sketch below (confirmed by everybody present)? You can't simply explain this by a better S-R ratio, but this is a clear proof of much enhanced resolution and light gathering power.

 

If you want to be scientific, every research that has been done on this subject confirms the 1,41x summation factor (Pirenne, Campbell and Green,...) and according to Meese et al. (2006) the improved S-R ratio, which you consider to be the only real gain, pushes this to even 1,8x.

 

I'm no scientist and prefer to leave the math to others, but I suggest you get in touch with Mr. Otte who teaches this kind of stuff at the Leiden University in Holland. He'd me more than happy to explain this into the smallest detail.

 

http://www.arieotte-binoscopes.nl/

 

Peter

 

NGC6905 (binoscope).jpg


Edited by PeterDob, 02 September 2017 - 08:43 AM.


#57 GlennLeDrew

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Posted 02 September 2017 - 05:39 PM

Peter,

Indeed, and as I've always stated, binocular summation does afford a 1.41x gain, as predicted by the integration of two similar images. And it applies to the unaided eye exactly as equally as it does for an arbitrarily large binocular. Aperture by itself plays no role. A ratio is a ratio, irrespective of the light collecting area.

 

And yes, I have, more times than I care to count, compared the one-eyed and two-eyed response, naked eye and with large binos. I've never once been given reason to suppose that the difference differs much from the root two gain. And most certainly not because of aperture.

 

Be wary of quantifying a difference that involves detecting vs not detecting; this leads to ludicrously large equivalent aperture ratios if one naively compares the apertures (it's not unlike division by zero). For instance, I might glimpse the California nebula with a 10X50 (2" aperture), whereas under the same conditions I might fail using a 16" Dob in mono mode. Does this mean that the bino is at least 16/2 = 8X larger in equivalent? If a 32" Dob were to do no better, do we then up-rate the aperture equivalent to 16X? Where would it end?

 

My point is that while the difference between seeing and not seeing is definitely profound, the fact of this occurring across a transitional boundary of the visual system response must not have accorded to it an unrealistic valuation.

 

My own magnitude limit determinations are in line with theory, being around 1/3 magnitude. And the degree of discrimination on subtle contrasts, as well as the improvement in detail discerned, are in accord. After 40 years of active astronomical observation I would hardly be classed an armchair theoritician. ;) I most certainly would not propound theory that my own experience did not support.



#58 PeterDob

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Posted 02 September 2017 - 07:13 PM

I only have 36 years of observing experience, but believe to be quite capable to tell the difference between impression and reality.

You talk about theory, but your theory is completely unsupported by scientific evidence. In my previous post I've mentioned three different scientific studies that prove you wrong. I've also given you the contact details of Mr. Otte, one of the World's leading authorities on binoscopes and binocular vision.

But if you won't even accept scientific proof, nor the word of people who know far more about it than you and me, then I see no point in continuing this conversation.

Peter

#59 Fomalhaut

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Posted 03 September 2017 - 04:15 AM

If I have understood properly, then according to Peter a binocular telescope will receive twice as much of light (what I don't oppose, but OTOH is distributed to two different eyes)  -  the optical perceptions of which are then superpositioned by the brain. Because the objectives' total area ist twice as large, the integrated perception of both eyes are added just like by increasing one mono-aperture by the factor of sqrt(2) ~1.41...

Glen's idea obviously superimposes the pictures as behold by the two eyes according to the same law of noise-reduction which in AP teaches 4 subs only to double the information of the final image or 2 subs resulting in an image with 1.41-times the information of one sub, what would correspond to increasing aperture of mono-scope only by a factor of sqrt(1.41) ~1.19.

I'm now suggesting the following test to verify in a simple way who is right:
Let's observe a globular cluster by means of a good monocular telescope firstly just as it is, using one eye only. Then secondly, by beam-splitting with a good bino-viewer, two-eyed and using same magnification as before.

If now Peter is right, M13 will reveal about the same information (same faint stars) in both configurations.
Or if Glen is right, then monocularly more information (fainter stars) should be perceived than binocularly (difference ~0.38 mag minus some slight loss by beam-splitter).

Hopefully I haven't messed it all up by not carefully enough reading all of what's been written already.

Chris


Edited by Fomalhaut, 03 September 2017 - 11:05 AM.


#60 PeterDob

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Posted 03 September 2017 - 05:09 AM

Dear Chris,

In theory your test could work perfectly well. Unfortunately there's no binoviewer up to the job because they all lose a lot of light (even the Siebert 2"). Perhaps in a SCT telescope which doesn't require an OCA. But in an SCT you have to move the primary forward a lot to get focus, which may also result in light loss.

 

EDIT: A better method would be to do a limiting magnitude test with a binoscope, with one and both eyes. The result would confirm an aperture 1,41x greater for binocular vision.

As far as I'm concerned and not mentioning the laboratory test results of the various studies I mentioned, the experience of a binoscope is so overwhelming that the significant gain in light, detail and contrast can't be explained merely by S-N ratio.

Peter


Edited by PeterDob, 03 September 2017 - 06:37 AM.


#61 Fomalhaut

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Posted 03 September 2017 - 06:37 AM

Hi Peter and Glen,

 

Back to my own post above, I have to admit I personally prefer a binoviewer on my frac when observing planets or the moon

and monocular vision (no binoviewer but twice as much light in the one ocular) for resolving globular clusters or other DSOs.

Best of all would of course be a real bino-scope consisting of two of my fracs...

 

(All of this has nothing to do with loyalty to Zarenski or Harrington, whose favoured "Adler-Index" I personally refuted in my CN-article "A new Performance Index for Binoculars" in 2015, by the way...)

 

Chris


Edited by Fomalhaut, 03 September 2017 - 06:51 AM.


#62 PeterDob

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Posted 03 September 2017 - 07:20 AM

Well, I had to agree with you. I've tried just about every binoviewer in search of the possibility to observe with both eyes without light loss. Unfortunately a binoviewer always turned out to be a compromise. Hence... the binoscope! :D

 

Cheers,

 

Peter 



#63 PETER DREW

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Posted 03 September 2017 - 09:23 AM

I don't have the theoretical background knowledge of some of the contributors but for what it's worth I do have over 60 years practical experience, 35 of them as a professional astronomical instrument maker with binocular telescopes a speciality.

Consequently this thread is of considerable interest to me and I would be disappointed if discussion turned to argument as this advances nothing. I certainly see benefits in using anything that permits the use of both eyes, be it comfort or perceived performance but I've not yet attempted any meaningful evaluation. I currently have 8", 10", 17" 20" and 30" Dobsonians and 80mm, 100mm, 150mm and 300mm binoscopes for comparison and am now motivated to do just that.    smile.gif 



#64 GlennLeDrew

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Posted 03 September 2017 - 10:05 AM

Binoviewers seem to lose a lot of light simply because of the fact of the light being split into two paths, thus halving the flux to each eye. Any half decent beam splitter designed for 50/50 transmission/reflection will deliver not much less than the full flux in total. And the other components likewise will induce small losses. If there is no notable difference in brightness between the two outputs, transmission for each side can easily be 45% (90% total) compared to the nominal (and of course unachievable) 50%. This is a small enough loss to not invalidate a test of limiting magnitude as outlined by Chris.



#65 PeterDob

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Posted 03 September 2017 - 12:10 PM

The main problem with a binoviewer is not the beamsplitter but its length. My 2" Siebert had a front aperture of 40mm but a lightpath length of 21cm (if I remember correctly), resulting in significant vignetting. You can do a simple daylight test, i.e. put your binoviewer in the focuser without OCA or eyepieces. Probably you will have difficulties seeing the edge of your primary and this is why they lose light. With a Newtonian (and also with most refractors) you use an OCA which narrows the light cone and lets most of the light through without vignetting. Also, without it you'll probably not be able to get the binoviewer to focus. Unfortunately, these OCAs protrude so far in the telescope that also they don't manage to capture all of the light cone and hence result in vignetting. Denk, Baader and Siebert are now offering 2" OCAs to solve that problem, but these still don't succeed in channeling all of the telescope's light to the eyepieces. Moreover, it is extremely difficult to make a perfect 2" negative lens and so these large OCAs suffer from edge distortion.

 

To round it off, an OCA adds at least 1,3x of magnification, so a direct comparison will never be possible. 

 

Peter



#66 GlennLeDrew

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Posted 03 September 2017 - 12:38 PM

Prism-based binoviewers can handle light cones as fast as about f/5-ish before axial aperture reduction commences, depending on the distance at which lies the eyepiece field stop from the rear prism aperture.

 

But even if aperture reduction is in effect with a fast scope, the same is occurring for both sides and so the test for limiting magnitude difference for one eye vs both is still fully valid.



#67 PeterDob

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Posted 03 September 2017 - 02:29 PM

Not really, because we're comparing monocular view (i.e. without binoviewer) to binocular (with binoviewer).

 

Peter



#68 GlennLeDrew

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Posted 03 September 2017 - 05:07 PM

Not really, because we're comparing monocular view (i.e. without binoviewer) to binocular (with binoviewer).

 

Peter

Oops! I thought I'd read one of Chris's tests to involve a binoviewer, looking through one eye then both. But then, this would be the same thing as using a true bino. Nonetheless, your typical f/7 and longer scope will most certainly not suffer axial aperture reduction.

 

I did some web surfing and turned up some number of hits on the topic of binocular summation. In the main, the consensus would seem to be a convergence toward the good ol' factor of 1.41 for S/N and information gain. CN's own bino guru Ed Zarenski looked into this via testing, and found gains that were of this order. Far more folks lean this way than those who advocate significantly larger gains.

 

As I pointed out earlier in this thread, a study that was linked to in this thread used brief flashes of dim light, which suggested a larger gain for bino summation. But I feel this is perhaps not quite relevant because normally we observe scenes which are of rather more steady light than flashing on for brief intervals then going off for longer spells. Given the already occasional perceiving when near the threshold, in which the object is lost in noise for some or most of the time, further reducing the opportunity to detect by having the target switched off some of the time might well accentuate the ratio of detection rates for two eyes vs one. In any event, using flashing targets surely is not representative of what we normally observe, and so such a test protocol should be treated with due caution.


Edited by GlennLeDrew, 03 September 2017 - 05:09 PM.


#69 PeterDob

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Posted 04 September 2017 - 03:28 AM

Zarenski is the ONLY one advocating 1,18x. As stated above, all scientific studies confirm 1,41x.

 

But what does it matter anyway... The main point is that everyone who's ever looked through a big binoscope was mesmerised by what they saw and that far larger monocular telescopes were unable to match detail, contrast, light and resolution. Just go to a star party and see where the longest queues are. Listen to the reactions of the people who've just taken a glance through a binoscope. 

 

A binoscope is a very complex instrument. It has some serious disadvantages and is not suitable for everyone. But it offers an experience unequalled by any other instrument.

 

Peter


Edited by PeterDob, 04 September 2017 - 03:34 AM.


#70 GlennLeDrew

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Posted 04 September 2017 - 03:56 AM

Peter,

Just to be certain of the units... A 1.41X gain in S/N and information is equivalent to a *linear* aperture increase of factor 1.189. Are your sources stating a *linear* aperture ratio of 1.41? (Which would be equivalent to a doubling of brightness.) That is not what I'm seeing in the great majority of published information I've gleaned thus far.



#71 PeterDob

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Posted 04 September 2017 - 04:21 AM

https://www.research...r_Visual_Acuity

 

As I said, I'm no technical expert. But the above-mentioned study seems to be the most comprehensive ever done on this subject. If you like, I can find a couple of others for you.

 

Peter


Edited by PeterDob, 04 September 2017 - 04:24 AM.

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#72 PETER DREW

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Posted 04 September 2017 - 06:11 AM

Regardless of how the figures are supported by theory or controlled practical experiment I think most observers who are able to use binocular vision would agree that the views with a binocular instrument are better than those of a similar aperture mono version, the degree of improvement would probably be on the YMMV principle. One could gain a similar "wow" factor by taking a telescope from a polluted site to a dark sky one.



#73 Gleb1964

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Posted 04 September 2017 - 08:59 AM

 

No, it equals a mono aperture 1,414x larger. Hence an 18" bino equals at least a 25" mono, both with regards to light gathering power and resolution. To my experience, on faint objects, you can even make that 30"-32", without having the much higher minimum magnification (due to exit pupil).

 

EDIT: 1,18x wouldn't be logical. A binoscope has twice the amount of aperture, so 1,414x the diameter of a monoscope.

Peter

Our visual system does not simply add the two images together to result in what would effectively be a doubling of brightness, which an effective increase in aperture of ratio 1.414 implies. The two images each contain their unique component of visual system noise, which is also integrated along with the two signals. The noise is averaged, and the signals are averaged, which results in the root two improvement in signal to noise.

 

Try to assess for yourself the differences in limiting magnitude at some selected exit pupil, with both eyes in use vs just one. I predict it will not differ much from 1/3 magnitude. As I noted, a 1.414 gain in signal to noise theoretically provides a boost to point source limiting magnitude of 0.37 magnitude, which corresponds to a linear aperture ratio of 1.189, which is an areal ratio of 1.414.

 

You and others are misconstruing the 1.414 figure for S/N gain, which equates to the same value in effective aperture *area*, for the *linear* aperture equivalent. A 19% increase in linear aperture provides 41% more area and hence 41% fainter detection. This is the result for our visual systems, just as it is for digital image integration of two same-exposure frames as done by legions of astro imagers.

 

The visceral improvement realized by two-eyed viewing might *seem* to suggest gains that could be equivalent to an aperture doubling, but both signal theory and direct observation that quantifies beyond the level of superficial impressions refute this.

 

Again, test your own stellar limiting magnitude...

 

Glenn explanation is right.

Just need to add that single aperture with linear factor of 1.189 and area factor of 1.41 have smaller Airy disc (in angular units) by the same linear and area factors, correspondingly. If maintain scale factor to keep constant size of disc Airy on detector, that means 2x factor of light density and 1.41 factor of signal to noise ration.


Edited by Gleb1964, 04 September 2017 - 09:01 AM.


#74 Jon Isaacs

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Posted 04 September 2017 - 09:21 AM

2) A binocular of the same aperture as a mono scope *does* afford a real gain in resolving power, by factor 19% when both eyes have similar capability. More correctly, shutting out one eye results in a loss of resolving power, it being 84% of two-eyed performance. With both eyes in operation one discriminates to a better degree what is present in the image. For instance, reading an eye chart is generally a bit easier with both eyes than for any any one of them alone.

 

 

I have to disagree.  Ultimately, the resolving power of the system is determined by the aperture and not the eye.  As long as magnifications sufficient for the eye to resolve the focal plane are used, I don't see how one can support a 19% increase in resolving power by using both eyes, the Rayleigh criteria is what it is because of the aperture limit, not because of the eye's limit. 

 

Jon Isaacs



#75 PeterDob

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Posted 04 September 2017 - 11:01 AM

Exactly, Jon! An even better test would be to measure the airy disk in a binocular system. This will confirm a linear aperture increase of 1,41x, as theory predicts.

Peter


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